Physiological and performance parameters associated with critical 
power decline in hypoxia among highly-trained endurance athletes

Tomasz Kowalski; Adrian Wilk; Kinga Rębiś; Jadwiga Malczewska-Lenczowska; Andrzej Klusiewicz; Tadej Debevec; Raphael Faiss

doi:10.5114/biolsport.2026.153530

eISSN: 2083-1862
ISSN: 0860-021X

Biology of Sport

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abstract:

Original paper

Physiological and performance parameters associated with critical power decline in hypoxia among highly-trained endurance athletes

Tomasz Kowalski

¹

,

Adrian Wilk

¹

,

Kinga Rębiś

¹

,

Jadwiga Malczewska-Lenczowska

²

,

Andrzej Klusiewicz

³

,

Tadej Debevec

^{4, 5}

,

Raphael Faiss

⁶

Department of Physiology, Institute of Sport—National Research Institute, Warsaw, Poland
Department of Nutrition Physiology, Institute of Sport—National Research Institute, Warsaw, Poland
Department of Physical Education and Health in Biala Podlaska, Faculty in Biala Podlaska, Jozef Pilsudski University of Physical Education, Warsaw, Poland
Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia
Department of Automatics, Biocybernetics and Robotics, “Jozef Stefan” Institute, Ljubljana, Slovenia
Institute of Sports Sciences, Faculty of Social and Political Sciences, University of Lausanne, Lausanne, Switzerland

Biol Sport. 2026;43:257–265

DOI: https://doi.org/10.5114/biolsport.2026.153530

Online publish date: 2025/08/29

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We sought to investigate whether the magnitude of differences in cycling critical power between normoxia and hypoxia (∆CP) is associated with fitness level or haematological status in highly trained endurance athletes. Thirty-three triathletes and longtrack speed skaters (11 females) completed two 3-minute CP cycling tests: one in normoxia (F_iO₂ = 20.8%) and the other in normobaric hypoxia (F_iO₂ = 14.2%). This cross-sectional study analysed ∆CP regarding performance, physiological, and haematological indices using correlation and regression analyses. Significant correlations were found between ∆CP and baseline CP in normoxia (r = -0.366, p = 0.047), V̇ O_2max (r = -0.437, p = 0.018), and MCH (r = 0.487, p = 0.012). Only a few significant associations were found between the indices obtained from venous blood sampling and ∆CP, different for females and males. In females, ∆CP was correlated with Hbmass (r = -0.761, p = 0.017), erythrocyte volume (r = -0.783, p = 0.013), plasma volume (r = -0.745, p = 0.021), and blood volume (r = -0.870, p = 0.002), all established with the CO rebreathing method. The best-performing regression model (R² = 0.501, RMSE = 0.033, p = 0.002, Cohen’s F² = 1.004) included MCH, V̇ O_2max, and Hb_mass. A higher fitness level is associated with a greater CP decrease in hypoxia among the homogeneous cohort of highly trained endurance athletes. Haematological status plays a more prominent role in females, and the CO rebreathing method should be considered a preferred approach for assessing haematological status in highly trained athletes.

keywords:

Physiological and performance parameters associated with critical power decline in hypoxia among highly-trained endurance athletes

Tomasz Kowalski 1 , Adrian Wilk 1 , Kinga Rębiś 1 , Jadwiga Malczewska-Lenczowska 2 , Andrzej Klusiewicz 3 , Tadej Debevec 4, 5 , Raphael Faiss 6

Cycling, Altitude, V̇ O2max, Haematological status, Haemoglobin mass

Tomasz Kowalski

¹

,

Adrian Wilk

¹

,

Kinga Rębiś

¹

,

Jadwiga Malczewska-Lenczowska

²

,

Andrzej Klusiewicz

³

,

Tadej Debevec

^{4, 5}

,

Raphael Faiss

⁶